U.S. patent number 10,516,174 [Application Number 15/579,666] was granted by the patent office on 2019-12-24 for metal sheet for separators of polymer electrolyte fuel cells, and metal sheet for manufacturing the same.
This patent grant is currently assigned to JFE STEEL CORPORATION. The grantee listed for this patent is JFE STEEL CORPORATION. Invention is credited to Shin Ishikawa, Chikara Kami, Takayoshi Yano.
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United States Patent |
10,516,174 |
Yano , et al. |
December 24, 2019 |
Metal sheet for separators of polymer electrolyte fuel cells, and
metal sheet for manufacturing the same
Abstract
A metal sheet for separators of polymer electrolyte fuel cells
comprises: a substrate made of metal; and a surface-coating layer
with which a surface of the substrate is coated, with a strike
layer in between, wherein a coating ratio of the strike layer on
the substrate is 2% to 70%, the strike layer is distributed in a
form of islands, and a maximum diameter of the islands of the
strike layer as coating portions is 1.00 .mu.m or less and is not
greater than a thickness of the surface-coating layer.
Inventors: |
Yano; Takayoshi (Tokyo,
JP), Ishikawa; Shin (Tokyo, JP), Kami;
Chikara (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
JFE STEEL CORPORATION |
Chiyoda-ku, Tokyo |
N/A |
JP |
|
|
Assignee: |
JFE STEEL CORPORATION
(Chiyoda-ku, Tokyo, JP)
|
Family
ID: |
57983661 |
Appl.
No.: |
15/579,666 |
Filed: |
July 29, 2016 |
PCT
Filed: |
July 29, 2016 |
PCT No.: |
PCT/JP2016/003526 |
371(c)(1),(2),(4) Date: |
December 05, 2017 |
PCT
Pub. No.: |
WO2017/026104 |
PCT
Pub. Date: |
February 16, 2017 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20180175401 A1 |
Jun 21, 2018 |
|
Foreign Application Priority Data
|
|
|
|
|
Aug 12, 2015 [JP] |
|
|
2015-159556 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
8/0228 (20130101); H01M 8/0215 (20130101); H01M
8/1018 (20130101); H01M 8/0202 (20130101); H01M
8/0206 (20130101); C23C 28/00 (20130101); C25D
7/06 (20130101); H01M 8/10 (20130101); C25D
3/562 (20130101); C25D 11/34 (20130101); C25D
5/12 (20130101); H01M 2008/1095 (20130101); C25D
3/48 (20130101); C25D 5/38 (20130101); C25D
3/40 (20130101); C25D 3/46 (20130101); C25D
15/00 (20130101); C25D 3/12 (20130101); C23C
18/1653 (20130101); C25D 5/36 (20130101) |
Current International
Class: |
H01M
8/0228 (20160101); H01M 8/1018 (20160101); H01M
8/0206 (20160101); H01M 8/0215 (20160101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2896499 |
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EP |
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3133682 |
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EP |
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3285319 |
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Feb 2018 |
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EP |
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H08180883 |
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JP |
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H10228914 |
|
Aug 1998 |
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JP |
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2006097088 |
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JP |
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Jan 2012 |
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JP |
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2012178324 |
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JP |
|
2013118096 |
|
Jun 2013 |
|
JP |
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2013243113 |
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Dec 2013 |
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JP |
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5700183 |
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5796694 |
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1020130004355 |
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KR |
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2011132797 |
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WO |
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Nov 2014 |
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WO |
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2015059857 |
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Apr 2015 |
|
WO |
|
Other References
Oct. 11, 2016, International Search Report issued in the
International Patent Application No. PCT/JP2016/003526. cited by
applicant .
Apr. 19, 2018, Partial Supplementary European Search Report (R 164
EPC) issued by the European Patent Office in the corresponding
European Patent Application No. 16834806.8. cited by applicant
.
Jun. 14, 2018, Extended European Search Report issued by the
European Patent Office in the corresponding European Patent
Application No. 16834806.8. cited by applicant .
Sep. 13, 2018, Office Action issued by the United States Patent and
Trademark Office in the U.S. Appl. No. 15/302,825. cited by
applicant .
Jun. 28, 2019, Office Action issued by the Korean Intellectual
Property Office in the corresponding Korean Patent Application No.
10-2018-7002472 with English language concise statement of
relevance. cited by applicant .
Dec. 21, 2018, Office Action issued by the Korean Intellectual
Property Office in the corresponding Korean Patent Application No.
10-2018-7002472 with English language concise statement of
relevance. cited by applicant.
|
Primary Examiner: Ridley; Basia A
Assistant Examiner: Chan; Heng M.
Attorney, Agent or Firm: Kenja IP Law PC
Claims
The invention claimed is:
1. A metal sheet for separators of polymer electrolyte fuel cells,
comprising: a substrate made of metal; and a surface-coating layer
with which a surface of the substrate is coated, with a strike
layer in between, wherein a coating ratio of the strike layer on
the substrate is 2% to 70%, the strike layer is distributed in a
form of islands, a maximum diameter of the islands of the strike
layer as coating portions is 1.00 .mu.m or less and is not greater
than a thickness of the surface-coating layer, the surface-coating
layer is formed on a surface of the strike layer, and is made of a
metal layer of Au, a metal oxide layer, a metal nitride layer, a
metal carbide layer, a carbon material layer, a conductive polymer
layer, an organic resin layer containing a conductive substance, or
a mixed layer thereof, and the strike layer contains at least one
element selected from the group consisting of Ni, Cu, and Ag.
2. The metal sheet for separators of polymer electrolyte fuel cells
according to claim 1, wherein the strike layer is made of an alloy
layer of Ni and P, and has a P content in a range of 5 mass % to 22
mass %.
3. The metal sheet for separators of polymer electrolyte fuel cells
according to claim 1, wherein the strike layer is a Ni layer, a Cu
layer, or a Ag layer.
Description
TECHNICAL FIELD
The disclosure relates to a metal sheet for separators of polymer
electrolyte fuel cells having excellent corrosion resistance and
adhesion property, and a metal sheet for manufacturing the
same.
BACKGROUND
In recent years, fuel cells that have excellent generation
efficiency and emit no CO.sub.2 are being developed for global
environment protection. Such a fuel cell generates electricity from
H.sub.2 and O.sub.2 through an electrochemical reaction. The fuel
cell has a sandwich-like basic structure, and includes an
electrolyte membrane (ion-exchange membrane), two electrodes (fuel
electrode and air electrode), gas diffusion layers of O.sub.2 (air)
and H.sub.2, and two separators.
Fuel cells are classified as phosphoric acid fuel cells, molten
carbonate fuel cells, solid oxide fuel cells, alkaline fuel cells,
and polymer electrolyte fuel cells (PEFC: proton-exchange membrane
fuel cells or polymer electrolyte fuel cells) according to the type
of electrolyte membrane used, which are each being developed.
Of these fuel cells, polymer electrolyte fuel cells have, for
example, the following advantages over other fuel cells.
(a) The fuel cell operating temperature is about 80.degree. C., so
that electricity can be generated at significantly low
temperature.
(b) The fuel cell body can be reduced in weight and size.
(c) The fuel cell can be started promptly, and has high fuel
efficiency and power density.
Polymer electrolyte fuel cells are therefore expected to be used as
power sources in electric vehicles, home or industrial stationary
generators, and portable small generators.
A polymer electrolyte fuel cell extracts electricity from H.sub.2
and O.sub.2 via a polymer membrane. As illustrated in FIG. 1, a
membrane-electrode joined body 1 is sandwiched between gas
diffusion layers 2 and 3 (for example, carbon paper) and separators
(bipolar plates) 4 and 5, forming a single component (a single
cell). An electromotive force is generated between the separators 4
and 5.
The membrane-electrode joined body 1 is called a membrane-electrode
assembly (MEA). The membrane-electrode joined body 1 is an assembly
of a polymer membrane and an electrode material such as carbon
black carrying a platinum catalyst on the front and back surfaces
of the membrane, and has a thickness of several 10 .mu.m to several
100 .mu.m. The gas diffusion layers 2 and 3 are often integrated
with the membrane-electrode joined body 1.
In the case of actually using polymer electrolyte fuel cells,
several tens to hundreds of single cells such as the above are
typically connected in series to form a fuel cell stack and put to
use.
The separators 4 and 5 are required to function not only as
(a) partition walls separating single cells,
but also as
(b) conductors carrying generated electrons,
(c) air passages 6 through which O.sub.2 (air) flows and hydrogen
passages 7 through which H.sub.2 flows, and
(d) exhaust passages through which generated water or gas is
exhausted (the air passages 6 or the hydrogen passages 7 also serve
as the exhaust passages).
The separators therefore need to have excellent durability and
electric conductivity.
Regarding durability, about 5000 hours are expected in the case of
using the polymer electrolyte fuel cell as a power source in an
electric vehicle, and about 40000 hours are expected in the case of
using the polymer electrolyte fuel cell as a home stationary
generator or the like. Since the proton conductivity of the polymer
membrane (electrolyte membrane) decreases if metal ions are eluted
due to corrosion, the separators need to be durable for long-term
generation.
Regarding electric conductivity, the contact resistance between the
separator and the gas diffusion layer is desirably as low as
possible, because an increase in contact resistance between the
separator and the gas diffusion layer causes lower generation
efficiency of the polymer electrolyte fuel cell. A lower contact
resistance between the separator and the gas diffusion layer
contributes to better power generation property.
Polymer electrolyte fuel cells using graphite as separators have
already been in practical use. The separators made of graphite are
advantageous in that the contact resistance is relatively low and
also corrosion does not occur. The separators made of graphite,
however, easily break on impact, and so are disadvantageous in that
the size reduction is difficult and the processing cost for forming
gas flow passages is high. These drawbacks of the separators made
of graphite hinder the widespread use of polymer electrolyte fuel
cells.
Attempts have been made to use a metal material as the separator
material instead of graphite. In particular, various studies have
been conducted to commercialize separators made of stainless steel,
titanium, a titanium alloy, or the like for enhanced
durability.
For example, JP H8-180883 A (PTL 1) discloses a technique of using,
as separators, a metal such as stainless steel or a titanium alloy
that easily forms a passive film.
JP H10-228914 A (PTL 2) discloses a technique of plating the
surface of a metal separator such as an austenitic stainless steel
sheet (SUS304) with gold to reduce the contact resistance and
ensure high output.
CITATION LIST
Patent Literatures
PTL 1: JP H8-180883 A
PTL 2: JP H10-228914 A
PTL 3: JP 2012-178324 A
PTL 4: JP 2013-118096 A
SUMMARY
Technical Problem
With the technique disclosed in PTL 1, however, the formation of
the passive film causes an increase in contact resistance, and
leads to lower generation efficiency. The metal material disclosed
in PTL 1 thus has problems such as high contact resistance and low
corrosion resistance as compared with the graphite material.
With the technique disclosed in PTL 2, a thin gold plating is hard
to be kept from the formation of pinholes, and a thick gold plating
is problematic in terms of an increase in cost.
In view of this, we previously proposed in JP 2012-178324 A (PTL 3)
"a metal sheet for separators of polymer electrolyte fuel cells
wherein a layer (hereafter also referred to as "Sn alloy layer")
made of a Sn alloy layer is formed on the surface of a substrate
made of metal and the layer includes conductive particles". Through
the development of the metal sheet for separators of polymer
electrolyte fuel cells described in PTL 3, we succeeded in
improving the corrosion resistance in the use environment of
separators of polymer electrolyte fuel cells.
However, the layer (hereafter also referred to as "surface-coating
layer") of the surface-coating layer such as the Sn alloy layer
formed on the surface of the metal material for separators of
polymer electrolyte fuel cells is required not only to have
predetermined corrosion resistance, but also to be thinner in terms
of reducing surface coating cost and improving manufacturability
(reduction in surface-coating layer formation time).
We accordingly proposed in JP 2013-118096 A (PTL 4) a surface
coating method for separators of fuel cells wherein the surface of
a substrate made of high Cr stainless steel is subjected to anodic
electrolysis that induces a Cr transpassive dissolution reaction
and then immediately subjected to Ni.sub.3Sn.sub.2 layer formation,
without the formation of an intermediate layer. We thus succeeded
in obtaining separators of polymer electrolyte fuel cells having
excellent corrosion resistance even in the case where the
surface-coating layer made of the Sn alloy layer such as the
Ni.sub.3Sn.sub.2 layer is made thinner.
In the fuel cell manufacturing process, high adhesion between the
substrate and the surface-coating layer is necessary so that the
surface-coating layer does not peel off the substrate. With the
technique described in PTL 4, however, the adhesion property is not
always sufficient, for example, in the process of forming the
separator into a desired shape, in the process of assembling the
fuel cell, or when the fuel cell vibrates violently during use, and
there is a possibility that the surface-coating layer peels.
Thus, while the surface-coating layer formed on the surface of the
substrate in the case of using a metal material such as stainless
steel as the material of separators of polymer electrolyte fuel
cells needs to have both corrosion resistance and adhesion property
as well as being thinner, such need has not been fulfilled
adequately.
It could therefore be helpful to provide a metal sheet for
separators of polymer electrolyte fuel cells having both excellent
corrosion resistance in the use environment of separators of
polymer electrolyte fuel cells and excellent adhesion property
between a substrate and a surface-coating layer even in the case
where the surface-coating layer is made thinner.
It could also be helpful to provide a metal sheet for manufacturing
the metal sheet for separators of polymer electrolyte fuel
cells.
Solution to Problem
We used various metal sheets as the material of separators of
polymer electrolyte fuel cells, and studied various surface-coating
layer formation processes for these metal sheets.
As a result, we made the following discoveries.
(1) First, to improve the adhesion property, we attempted to form a
strike layer made of a metal layer of Ni, Cu, or the like as a base
layer on the surface of a substrate made of metal, prior to the
formation of a surface-coating layer. We then discovered that
forming the strike layer as the base layer on the surface of the
metal substrate significantly improves the adhesion property of the
surface-coating layer.
(2) Next, we attempted to form a thinner surface-coating layer
after forming the strike layer, and discovered the following. When
the surface-coating layer is made thinner, defects from the
surface-coating layer to the metal substrate increase, and the
strike layer is continuously corroded through these defects. This
causes the surface-coating layer above the strike layer to
exfoliate, exposing the metal substrate to the separator use
environment. As a result, the corrosion resistance degrades
significantly.
(3) We carried out further research to prevent the degradation of
the corrosion resistance in the case of making the surface-coating
layer thinner.
We consequently discovered the following: By limiting the coating
ratio (coverage factor) of the strike layer on the substrate to the
range of 2% to 70% and also limiting the coating form of the strike
layer so that the strike layer is distributed in the form of
islands and the maximum diameter of the island-like coating
portions of the strike layer is 1.00 .mu.m or less and is not
greater than the thickness of the surface-coating layer formed on
the strike layer, the continuous corrosion of the strike layer is
suppressed, and as a result the degradation of the corrosion
resistance associated with the exfoliation of the surface-coating
layer is effectively prevented and the adhesion property is further
enhanced.
(4) The reason why limiting the coating ratio of the strike layer
on the substrate and the coating form of the strike layer as
mentioned above suppresses the continuous corrosion of the strike
layer is considered as follows.
By limiting the coating ratio of the strike layer on the substrate
to the range of 2% to 70%, a discontinuous portion such as a
non-coating area of the strike layer appears on the surface of the
metal substrate, and this discontinuous portion of the strike layer
acts as an area that inhibits the propagation of the corrosion.
Hence, the continuous corrosion of the strike layer can be
suppressed even in the case where the surface-coating layer is made
thinner.
Moreover, by limiting the coating form of the strike layer so that
the strike layer is distributed in the form of islands and the
maximum diameter of the island-like coating portions of the strike
layer is 1.00 .mu.m or less and is not greater than the thickness
of the surface-coating layer, discontinuous portions such as
non-coating areas of the strike layer are formed throughout the
surface of the substrate, as a result of which the degradation of
the corrosion resistance can be prevented more effectively. This
also makes the whole interface between the metal substrate and the
surface-coating layer rough, and so ensures higher adhesion
property by the anchor effect.
(5) We also discovered that, while the strike layer may be a metal
layer of Ni, Cu, Ag, Au, or the like or an alloy layer containing
at least one selected from these elements, a Ni--P strike layer
made of an alloy layer of Ni and P is particularly suitable as the
strike layer for its low material cost and excellent corrosion
resistance. We further discovered that, by limiting the P content
in the Ni--P strike layer to the range of 5 mass % to 22 mass %,
excellent corrosion resistance can be maintained more stably even
in the event of long exposure to high potential in the separator
use environment.
The reason for this is considered as follows. By limiting the P
content in the Ni--P strike layer to the range of 5 mass % to 22
mass %, a more stable Ni--P compound in the separator use
environment is formed, with it being possible to further suppress
the corrosion of the strike layer.
(6) We additionally discovered that, in the case where the
surface-coating layer is a Sn alloy layer, coating the surface of
the layer with a Sn-containing oxide layer further improves the
corrosion resistance.
The reason for this is considered as follows. Since the
Sn-containing oxide layer is very stable in the separator use
environment, coating the surface of the Sn alloy layer with the
Sn-containing oxide layer suppresses the corrosion of the Sn alloy
layer effectively. The corrosion resistance can be further improved
by such an effect.
The disclosure is based on the aforementioned discoveries.
We thus provide:
1. A metal sheet for separators of polymer electrolyte fuel cells,
comprising: a substrate made of metal; and a surface-coating layer
with which a surface of the substrate is coated, with a strike
layer in between, wherein a coating ratio of the strike layer on
the substrate is 2% to 70%, the strike layer is distributed in a
form of islands, and a maximum diameter of the islands of the
strike layer as coating portions is 1.00 .mu.m or less and is not
greater than a thickness of the surface-coating layer.
2. The metal sheet for separators of polymer electrolyte fuel cells
according to 1., wherein the strike layer contains at least one
element selected from the group consisting of Ni, Cu, Ag, and
Au.
3. The metal sheet for separators of polymer electrolyte fuel cells
according to 1., wherein the strike layer is made of an alloy layer
of Ni and P, and has a P content in a range of 5 mass % to 22 mass
%.
4. The metal sheet for separators of polymer electrolyte fuel cells
according to any one of 1. to 3., wherein the surface-coating layer
is made of a metal layer, an alloy layer, a metal oxide layer, a
metal nitride layer, a metal carbide layer, a carbon material
layer, a conductive polymer layer, an organic resin layer
containing a conductive substance, or a mixed layer thereof.
5. The metal sheet for separators of polymer electrolyte fuel cells
according to any one of 1. to 3., wherein the surface-coating layer
is a layer made of a Sn alloy layer, and the metal sheet for
separators of polymer electrolyte fuel cells further comprises a
Sn-containing oxide layer on a surface of the surface-coating
layer.
6. A metal sheet for manufacturing the metal sheet for separators
of polymer electrolyte fuel cells according to any one of 1. to 5.,
comprising: a substrate made of metal; and a strike layer on a
surface of the substrate, wherein a coating ratio of the strike
layer on the substrate is 2% to 70%, the strike layer is
distributed in a form of islands, and a maximum diameter of the
islands of the strike layer as coating portions is 1.00 .mu.m or
less.
Advantageous Effect
It is possible to obtain a separator of a fuel cell having
excellent corrosion resistance and adhesion property, and thus
obtain a polymer electrolyte fuel cell having excellent durability
at low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a schematic diagram illustrating the basic structure of a
fuel cell.
DETAILED DESCRIPTION
Detailed description is given below.
(1) Metal Sheet Used as Substrate
A metal sheet used as a substrate in the disclosure is not limited,
but a stainless steel sheet (ferritic stainless steel sheet,
austenitic stainless steel sheet, dual-phase stainless steel
sheet), a titanium sheet, a titanium alloy sheet, and the like
having excellent corrosion resistance are particularly
advantageous.
For example, as the stainless steel sheet, SUS447J1 (Cr: 30 mass %,
Mo: 2 mass %), SUS445J1 (Cr: 22 mass %, Mo: 1 mass %), SUS443J1
(Cr: 21 mass %), SUS439 (Cr: 18 mass %), SUS316L (Cr: 18 mass %,
Ni: 12 mass %, Mo: 2 mass %), or the like is suitable. SUS447J1
containing about 30 mass % Cr has high corrosion resistance, and so
is particularly advantageous as the substrate for separators of
polymer electrolyte fuel cells used in an environment where high
corrosion resistance is required. As the titanium sheet, JIS 1 type
or the like is suitable. As the titanium alloy sheet, JIS 61 type
or the like is suitable.
In view of the installation space or weight when stacking fuel
cells, the sheet thickness of the metal sheet for separators is
preferably in the range of 0.03 mm to 0.30 mm. If the sheet
thickness of the metal sheet for separators is less than 0.03 mm,
the production efficiency of the metal sheet decreases. If the
sheet thickness of the metal sheet for separators is more than 0.30
mm, the installation space or weight when stacking fuel cells
increases. The sheet thickness of the metal sheet for separators is
more preferably 0.03 mm or more and 0.10 mm or less.
(2) Surface-Coating Layer
A surface-coating layer with which the surface of the substrate is
coated is not limited, but a material excellent in corrosion
resistance and conductivity in the use environment (pH: 3 (sulfuric
acid environment), use temperature: 80.degree. C.) of separators of
polymer electrolyte fuel cells is preferably used. For example, a
metal layer, an alloy layer, a metal oxide layer, a metal carbide
layer, a metal nitride layer, a carbon material layer, a conductive
polymer layer, an organic resin layer containing a conductive
substance, or a mixed layer thereof is suitable.
Examples of the metal layer include metal layers of Au, Ag, Cu, Pt,
Pd, W, Sn, Ti, Al, Zr, Nb, Ta, Ru, Ir, and Ni. A metal layer of Au
or Pt is particularly suitable.
Examples of the alloy layer include Sn alloy layers of Ni--Sn
(Ni.sub.3Sn.sub.2, Ni.sub.3Sn.sub.4), Cu--Sn (Cu.sub.3Sn,
Cu.sub.6Sn.sub.5), Fe--Sn (FeSn, FeSn.sub.2), Sn--Ag, and Sn--Co,
and alloy layers of Ni--W, Ni--Cr, and Ti--Ta. An alloy layer of
Ni--Sn or Fe--Sn is particularly suitable.
Examples of the metal oxide layer include metal oxide layers of
SnO.sub.2, ZrO.sub.2, TiO.sub.2, WO.sub.3, SiO.sub.2,
Al.sub.2O.sub.3, Nb.sub.2O.sub.5, IrO.sub.2, RuO.sub.2, PdO.sub.2,
Ta.sub.2O.sub.5, Mo.sub.2O.sub.5, and Cr.sub.2O.sub.3. A metal
oxide layer of TiO.sub.2 or SnO.sub.2 is particularly suitable.
Examples of the metal nitride layer and the metal carbide layer
include metal nitride layers and metal carbide layers of TiN, CrN,
TiCN, TiAlN, AlCrN, TiC, WC, SiC, B.sub.4C, molybdenum nitride,
CrC, TaC, and ZrN. A metal nitride layer of TiN is particularly
suitable.
Examples of the carbon material layer include carbon material
layers of graphite, diamond, amorphous carbon, diamond-like carbon,
carbon black, fullerene, and carbon nanotube. A carbon material
layer of graphite or diamond-like carbon is particularly
suitable.
Examples of the conductive polymer layer include conductive polymer
layers of polyaniline and polypyrrole.
The organic resin layer containing a conductive substance contains
at least one conductive substance selected from a metal, an alloy,
a metal oxide, a metal nitride, a metal carbide, a carbon material,
and a conductive polymer included in the aforementioned metal
layer, alloy layer, metal oxide layer, metal nitride layer, metal
carbide layer, carbon material layer, and conductive polymer layer,
and contains at least one organic resin selected from epoxy resin,
phenol resin, polyamide-imide resin, polyester resin, polyphenylene
sulfide resin, polyamide resin, urethane resin, acrylic resin,
polyethylene resin, polypropylene resin, carbodiimide resin, phenol
epoxy resin, and the like. As the organic resin layer containing a
conductive substance, for example, graphite-dispersed phenol resin
or carbon black-dispersed epoxy resin is suitable.
As the conductive substance, a metal and a carbon material (in
particular, graphite, carbon black) are suitable. The content of
the conductive substance is not limited, as long as predetermined
conductivity is obtained in separators of polymer electrolyte fuel
cells.
Examples of the mixed layer include a mixed layer of a
TiN-dispersed Ni--Sn alloy.
For the formation of the surface-coating layer on the surface of
the metal substrate, a method such as plating, physical vapor
deposition (PVD), chemical vapor deposition (CVD),
electrodeposition, thermal spraying, surface melting treatment, or
coating may be used depending on the type of the surface-coating
layer to be formed.
For example, in the case of providing the surface-coating layer
that is the metal layer or the alloy layer, plating is suitable. In
this case, by a conventionally known plating method the substrate
is immersed in a plating bath adjusted to a predetermined
composition and subjected to electroplating, electroless plating,
or hot dip coating. The thickness of such a surface-coating layer
is preferably 0.1 .mu.m or more and 5.0 .mu.m or less. If the
thickness of the surface-coating layer is less than 0.1 .mu.m,
coating defects increase and the corrosion resistance tends to
degrade. If the thickness of the surface-coating layer is more than
5.0 .mu.m, the coating cost increases and manufacturability
decreases. The thickness of the surface-coating layer is more
preferably 0.5 .mu.m or more. The thickness of the surface-coating
layer is more preferably 3.0 .mu.m or less.
In the case of providing the metal oxide layer, the metal nitride
layer, the metal carbide layer, or the carbon material layer,
physical vapor deposition (PVD) or chemical vapor deposition (CVD)
is suitable. The thickness of such a surface-coating layer is
preferably in the range of 0.05 .mu.m to 1.0 .mu.m, for the same
reason as above.
In the case of providing the conductive polymer layer,
electropolymerization is suitable. The thickness of such a
surface-coating layer is preferably in the range of 0.1 .mu.m to
5.0 .mu.m, for the same reason as above.
In the case of providing the organic resin layer containing a
conductive substance, coating (a method of applying a predetermined
coating solution and then firing) is suitable. The thickness of
such a surface-coating layer is preferably in the range of 1.0
.mu.m to 50.0 .mu.m, for the same reason as above. The thickness of
the surface-coating layer is more preferably 1.0 .mu.m or more. The
thickness of the surface-coating layer is more preferably 10.0
.mu.m or less.
(Strike Layer)
Forming a strike layer between the metal substrate and the
surface-coating layer improves the adhesion between the
surface-coating layer and the substrate. The reason why forming the
strike layer between the metal substrate and the surface-coating
layer improves the adhesion between the surface-coating layer and
the substrate is considered as follows.
In the case where there is no strike layer, an inactive passive
film or the like tends to be formed on the surface of the metal
substrate, making it difficult to achieve high adhesion. In the
case where the strike layer is provided, on the other hand, the
formation of the passive film or the like is suppressed and the
surface of the metal substrate is kept from becoming inactive, as a
result of which the adhesion between the substrate and the
surface-coating layer is improved.
Moreover, a strike layer whose surface is uneven is more
advantageous because the adhesion is further improved by the anchor
effect.
The disclosed metal sheet for separators of polymer electrolyte
fuel cells thus has excellent adhesion between the substrate and
the surface-coating layer, and therefore is advantageous in the
process of forming the separator into a desired shape or the
process of assembling the fuel cell where high adhesion is
required, or when the fuel cell vibrates violently during use.
It is very important to limit the coating ratio of the strike layer
on the substrate and the coating form of the strike layer as
follows: the coating ratio of the strike layer on the substrate: 2%
to 70%.
By limiting the coating ratio of the strike layer on the substrate
to this range, the corrosion resistance in the separator use
environment can be maintained even in the case where the
surface-coating layer is made thinner. The reason for this is
considered as follows.
Typically, when the thickness of the surface-coating layer is
reduced, in-layer defects from the surface-coating layer to the
substrate increase. Through these defects, the strike layer between
the metal substrate and the surface-coating layer is widely
corroded continuously in the surface direction, causing the
surface-coating layer above the strike layer to exfoliate from the
metal substrate. When the surface-coating layer exfoliates, the
substrate is exposed to the separator use environment, and as a
result the corrosion resistance decreases.
Limiting the coating ratio of the strike layer on the substrate to
the aforementioned range, however, allows the strike layer to be
formed discontinuously on the surface of the substrate. In other
words, a discontinuous portion such as a non-coating area of the
strike layer appears in part of the surface of the substrate. This
discontinuous portion of the strike layer acts as an area that
inhibits the propagation of the corrosion. Hence, the continuous
corrosion of the strike layer is suppressed even in the case where
the surface-coating layer is made thinner. The degradation of the
corrosion resistance can be prevented in this way.
If the coating ratio of the strike layer on the substrate is less
than 2%, the adhesion between the metal substrate and the
surface-coating layer decreases. If the coating ratio of the strike
layer on the substrate is more than 70%, the corrosion resistance
cannot be maintained in the case where the thickness of the
surface-coating layer is reduced. Accordingly, the coating ratio of
the strike layer on the substrate is limited to the range of 2% to
70%. The coating ratio of the strike layer on the substrate is
preferably 5% or more. The coating ratio of the strike layer on the
substrate is preferably 60% or less. The coating ratio of the
strike layer on the substrate is more preferably 10% or more. The
coating ratio of the strike layer on the substrate is more
preferably 50% or less. The coating ratio of the strike layer on
the substrate is further preferably 15% or more. The coating ratio
of the strike layer on the substrate is further preferably 40% or
less. the strike layer being distributed in the form of islands and
the maximum diameter of the island-like coating portions of the
strike layer being 1.00 .mu.m or less and being not greater than
the thickness of the surface-coating layer.
The strike layer needs to have a coating form in which the strike
layer is distributed in the form of islands on the surface of the
substrate and the maximum diameter of the island-like coating
portions of the strike layer is 1.00 .mu.m or less.
By limiting the coating form of the strike in this way,
discontinuous portions such as non-coating areas of the strike
layer are formed throughout the surface of the substrate. This
suppresses the continuous corrosion of the strike layer more
effectively, and prevents the degradation of the corrosion
resistance more effectively. This also makes the whole interface
between the metal substrate and the surface-coating layer rough,
and so enhances the adhesion property by the anchor effect. Here,
if the maximum diameter of the island-like coating portions is
greater than the thickness of the surface-coating layer, the
discontinuity of the strike layer with respect to the thickness of
the surface-coating layer decreases relatively, and the corrosion
resistance cannot be maintained. The maximum diameter of the
island-like coating portions therefore needs to be not greater than
the thickness of the surface-coating layer. The thickness of the
surface-coating layer mentioned here is the average thickness of
the surface-coating layer.
Thus, the coating form of the strike layer is limited so that the
strike layer is distributed in the form of islands on the surface
of the substrate and the maximum diameter of the island-like
coating portions of the strike layer is 1.00 .mu.m or less and is
not greater than the thickness of the surface-coating layer.
The maximum diameter of the island-like coating portions of the
strike layer is preferably limited to 0.50 .mu.m or less and not
greater than the thickness of the surface-coating layer. The
maximum diameter of the island-like coating portions of the strike
layer is more preferably limited to 0.10 .mu.m or less and not
greater than the thickness of the surface-coating layer.
The specific shape of each island-like coating portion is not
limited, and may be any of circular, elliptic, polygonal, ameboid
(a shape extending in a plurality of irregular directions), etc.
The diameter of each island-like coating portion is defined as the
diameter of the smallest circle that touches two or more points on
the perimeter of the island-like coating portion and completely
encloses the island-like coating portion.
The strike layer is preferably a metal layer of Ni, Cu, Ag, Au, or
the like or an alloy layer containing at least one selected from
these elements. A Ni strike or a Ni--P strike made of an alloy
layer of Ni and P is more preferable in terms of material cost.
In the case of a Ni--P strike, it is further preferable to limit
the P content in the Ni--P strike layer to the range of 5 mass % to
22 mass %.
P content in Ni--P strike layer: 5 mass % to 22 mass %
By limiting the P content in the Ni--P strike layer to this range,
excellent corrosion resistance can be maintained more stably even
in the event of long exposure to high potential in the separator
environment. The reason for this is considered as follows.
By limiting the P content in the Ni--P strike layer to the range of
5 mass % to 22 mass %, a more stable Ni--P compound in the
separator use environment is formed, with it being possible to
suppress the corrosion of the strike layer effectively for a longer
time.
If the P content in the Ni--P strike layer is less than 5 mass %,
the improvement effect is insufficient. If the P content in the
Ni--P strike layer is more than 22 mass %, the composition of the
Ni--P strike tends to be not uniform. Such a range is also not
preferable in terms of maintaining excellent corrosion resistance
in the event of long exposure to high potential in the separator
environment. Therefore, the P content in the Ni--P strike layer is
preferably limited to the range of 5 mass % to 22 mass %. The P
content in the Ni--P strike layer is more preferably 7 mass % or
more. The P content in the Ni--P strike layer is more preferably 20
mass % or less. The P content in the Ni--P strike layer is further
preferably 10 mass % or more. The P content in the Ni--P strike
layer is further preferably 18 mass % or less.
The method of forming the strike layer may be a conventionally
known plating method whereby electroplating or electroless plating
is performed in a plating bath adjusted to an appropriate
composition. For example in the case of electroplating, to limit
the coating form of the strike layer as mentioned above, the time
of retention in the plating bath, i.e. the electroplating time, and
the current density during electroplating need to be controlled
appropriately.
The electroplating time and the current density during
electroplating influence the coating ratio of the strike layer on
the substrate, and the current density during electroplating also
influences the maximum diameter of the island-like coating
portions. When the electroplating time is longer and the current
density is higher, the coating ratio of the strike layer on the
substrate is higher. Moreover, a higher current density typically
facilitates nucleation, which contributes to a smaller maximum
diameter of the island-like coating portions.
For example, in the case of forming a Ni strike, a Ni--P strike, or
a Cu strike, a current density of 6 A/dm.sup.2 or more and an
electroplating time of 1 second or more are preferable in terms of
achieving the desired coating form, although fine adjustment is
needed for differences depending on the structure of the
electroplating apparatus such as the distance between electrodes
and the size of the plating tank. A current density of 7 A/dm.sup.2
or more and an electroplating time of 1 second or more are more
preferable. If the current density is excessively high, the
adhesion decreases. The upper limit of the current density is
therefore preferably about 10 A/dm.sup.2. The electroplating time
is preferably 180 seconds or less. The electroplating time is more
preferably 60 seconds or less.
In the case of forming an Ag strike or an Au strike, on the other
hand, a current density of 4 A/dm.sup.2 or more and an
electroplating time of 1 second or more are preferable. A current
density of 5 A/dm.sup.2 or more and an electroplating time of 1
second or more are more preferable. If the current density is
excessively high, the adhesion decreases. The upper limit of the
current density is therefore preferably about 10 A/dm.sup.2. The
electroplating time is preferably 180 seconds or less. The
electroplating time is more preferably 60 seconds or less.
The P content in the Ni--P strike layer is adjustable by the P
concentration in the plating bath or the current density in
plating.
(4) Sn-Containing Oxide Layer
In the disclosed metal sheet for separators, in the case where the
surface-coating layer is a layer (Sn alloy layer) made of a Sn
alloy layer, the surface of the Sn alloy layer is preferably coated
with a Sn-containing oxide layer. This further improves the
corrosion resistance for long time use in the separator use
environment.
The Sn-containing oxide layer with which the surface of the Sn
alloy layer is coated is not a natural oxide layer created in the
atmospheric environment but an oxide layer deliberately formed by a
process such as immersion in an acid solution. The thickness of the
natural oxide layer is typically about 2 nm to 3 nm.
The main component of the Sn-containing oxide layer is preferably
SnO.sub.2. The thickness of the Sn-containing oxide layer is
preferably 5 nm or more. The thickness of the Sn-containing oxide
layer is preferably 100 nm or less. The thickness of the
Sn-containing oxide layer is more preferably 10 nm or more. The
thickness of the Sn-containing oxide layer is more preferably 30 nm
or less. If the Sn-containing oxide layer is excessively thick, the
conductivity decreases. If the Sn-containing oxide layer is
excessively thin, the corrosion resistance improvement effect in
the separator use environment cannot be achieved.
The reason why coating the surface of the Sn alloy layer with the
Sn-containing oxide layer improves the corrosion resistance for
long time use in the separator use environment is considered as
follows. Since the Sn-containing oxide layer is very stable in the
separator use environment, coating the surface of the
surface-coating layer with the Sn-containing oxide layer suppresses
the corrosion of the surface-coating layer effectively.
Here, the oxide layer is deliberately formed by a process such as
immersion in an acid solution instead of using a natural oxide
layer, for the following reason. Through such a process, the oxide
layer can be uniformly and accurately formed on the surface of the
surface-coating layer, with it being possible to suppress the
corrosion of the surface-coating layer very effectively.
The Sn-containing oxide layer may be formed by a method of
immersion in an acid aqueous solution having oxidizability such as
hydrogen peroxide or nitric acid, or a method of anodic
electrolysis.
For example, the Sn-containing oxide layer can be formed by
applying anodic electrolysis, in a sulfuric acid aqueous solution
of a temperature of 60.degree. C. and a pH of 1, to the metal sheet
for separators having the surface-coating layer for 5 minutes with
a current density of +1 mA/cm.sup.2.
The method of forming the Sn-containing oxide layer is not limited
to the above. Other examples include physical vapor deposition
(PVD), chemical vapor deposition (CVD), and coating.
(5) Other Features
After forming the surface-coating layer on the surface of the metal
substrate with the strike layer in between or after forming the Sn
alloy layer on the surface of the metal substrate with the strike
layer in between and then forming the Sn-containing oxide layer, a
conductive layer with lower electric resistance may be further
formed on the surface-coating layer or the Sn-containing oxide
layer, to improve the conductivity which is one of the required
properties of separators. For example, the surface-coating layer or
the Sn-containing oxide layer may be coated with a metal layer, a
conductive polymer layer, an alloy layer including conductive
particles, or a polymer layer including conductive particles, in
order to reduce the contact resistance.
EXAMPLES
Separators of polymer electrolyte fuel cells are used in a severe
corrosion environment of about 80.degree. C. in temperature and 3
in pH, and therefore excellent corrosion resistance is required.
Moreover, high adhesion between the metal substrate and the
surface-coating layer is required so that the surface-coating layer
does not peel off the metal substrate in the fuel cell
manufacturing process such as the process of forming the separator
into a desired shape or the process of assembling the fuel cell. In
view of these required properties, the following two types of
evaluation were conducted on the below-mentioned samples.
(1) Evaluation of Corrosion Resistance (Stability in Separator Use
Environment)
Each sample was immersed in a sulfuric acid aqueous solution of a
temperature of 80.degree. C. and a pH of 3 and subjected to the
application of a constant potential of 0.9 V (vs. SHE) for 100
hours using Ag/AgCl (saturated KCl aqueous solution) as a reference
electrode, and the total electric charge conducted for 100 hours
was measured. Based on the total electric charge conducted for 100
hours, the corrosion resistance after 100 hours in the separator
use environment was evaluated by the following criteria. Excellent:
the total electric charge conducted for 100 hours was less than 15
mC/cm.sup.2. Good: the total electric charge conducted for 100
hours was 15 mC/cm.sup.2 or more and less than 100 mC/cm.sup.2.
Poor: the total electric charge conducted for 100 hours was 100
mC/cm.sup.2 or more.
(2) Evaluation of Adhesion Property
The adhesive face of Scotch tape was adhered to the surface of each
sample obtained by forming a surface-coating layer on the surface
of a metal substrate, in an area of 20 mm.times.20 mm. The Scotch
tape was then removed, and the adhesion property was evaluated by
the following criteria. Good: the surface-coating layer did not
peel after the removal of the Scotch tape. Poor: the
surface-coating layer peeled after the removal of the Scotch
tape.
Example 1
Each of SUS447J1 (Cr: 30 mass %) of 0.05 mm in sheet thickness and
titanium JIS 1 type of 0.05 mm in sheet thickness as a substrate
was subjected to appropriate pretreatment such as degreasing, and
then a strike layer with the coating form listed in Table 1 was
formed on the substrate using the plating bath composition and
plating condition listed in Table 1 and mentioned below. Next, a
surface-coating layer with the average thickness listed in Table 1
was formed on the substrate having the strike layer, to obtain a
metal sheet for separators.
For the metal layer and alloy layer of Au and Ni.sub.3Sn.sub.2 and
TiN-dispersed Ni.sub.3Sn.sub.2, the surface-coating layer was
formed using the below-mentioned plating bath composition and
plating condition. For the metal oxide layers of TiO.sub.2 and
SnO.sub.2, the surface-coating layer was formed by physical vapor
deposition (PVD). For the metal nitride layer (TiN), the
surface-coating layer was formed by physical vapor deposition
(PVD). For the carbon material layer (diamond-like carbon), the
surface-coating layer was formed by chemical vapor deposition
(CVD). For the conductive polymer layer (polyaniline), the
surface-coating layer was formed by electropolymerization. For the
organic resin layer containing a conductive substance (carbon
black-dispersed epoxy resin and graphite-dispersed phenol resin),
the surface-coating layer was formed by applying a predetermined
coating solution and then firing.
The carbon black-dispersed epoxy resin was obtained by dispersing
carbon black particles with an average particle size of 50 nm in
epoxy resin in a proportion of 20 mass %. The graphite-dispersed
phenol resin was obtained by dispersing graphite particles with an
average particle size of 3 .mu.m in phenol resin in a proportion of
20 mass %.
In samples Nos. 45 and 47 to 50, the obtained metal sheet for
separators was subjected to anodic electrolysis in a sulfuric acid
aqueous solution of a temperature of 60.degree. C. and a pH of 1
for 5 minutes with a current density of +1 mA/cm.sup.2, to form a
Sn-containing oxide layer on the surface of the surface-coating
layer.
Each property was evaluated in the aforementioned manner using the
obtained metal sheet for separators.
The coating form of the strike layer was regulated by determining
the relationship with the electroplating time and the current
density beforehand. The average thickness of the surface-coating
layer and the average thickness of the Sn-containing oxide layer
were each regulated by determining the relationship with the
plating time, the anodic electrolysis time, the layer formation
time in physical vapor deposition (PVD) or chemical vapor
deposition (CVD), and the amount of the coating solution applied in
the coating beforehand. For comparison, a metal sheet for
separators having no strike layer was also prepared, and each
property was evaluated in the aforementioned manner.
The coating ratio of the strike layer on the substrate and the
maximum diameter of the island-like coating portions were measured
by the following method.
First, each sample obtained by forming the strike layer on the
surface of the substrate (0.05 mm in thickness) was cut to about 10
mm W.times.10 mm L. The coating form of the strike layer was
observed using a scanning electron microscope (SEM), and the
diameter of each island-like coating portion was measured and the
maximum value of the diameters was determined.
Next, the coating portion and non-coating portion of the strike
layer were binarized using image analysis software, to calculate
the coating ratio of the strike layer on the substrate. Although
the magnification in the SEM observation may be freely changed
according to the maximum diameter of the coating portions, the
magnification is preferably about 10000 to 100000.
The measurement of each of the coating ratio of the strike layer on
the substrate and the diameter of each island-like coating portion
was performed on 10 samples obtained by cutting the same sample
having the strike layer to the aforementioned shape. The coating
ratio of the strike layer on the substrate is the average coating
ratio of the strike layer on the substrate of the 10 samples, and
the maximum diameter of the island-like coating portions is the
maximum value of the diameters of the island-like coating portions
observed in the 10 samples.
Here, the composition of the strike made of an alloy layer of Ni
and P was measured by an energy-dispersive X-ray spectrometer (EDX)
used in the SEM observation.
Regarding the samples having no strike, "-" is shown in the fields
of the coating ratio of the strike layer on the substrate and the
maximum diameter of the island-like coating portion of the strike
layer in Table 1.
The average thickness of the surface-coating layer was measured by
the following method. The measurement method in the case where the
average thickness is 1.0 .mu.m or more is described first. Each
sample obtained by forming the strike layer and the surface-coating
layer on the surface of the substrate (0.05 mm in thickness) was
cut to about 10 mm W.times.15 mm L. The sample was then embedded in
resin, polished in the cross section, and then observed using a
scanning electron microscope (SEM) to measure the thickness of the
surface-coating layer. The measurement of the thickness of the
surface-coating layer was performed on 10 samples obtained by
cutting the same sample having the surface-coating layer to the
aforementioned shape, and the average thickness of these samples
was set as the average thickness of the surface-coating layer.
The measurement method in the case where the average thickness of
the surface-coating layer is less than 1.0 .mu.m and the method of
measuring the average thickness of the Sn-containing oxide layer
are described next. Each sample obtained by forming the strike
layer and the surface-coating layer and, for Nos. 45 and 47 to 50,
further the Sn-containing oxide layer on the surface of the
substrate (0.05 mm in thickness) was processed by a focused ion
beam to prepare a thin film for cross-section observation. The
produced thin film for cross-section observation was then observed
using a transmission electron microscope (TEM), to measure the
average thickness of each of the surface-coating layer and the
Sn-containing oxide layer. In the measurement of the average
thickness of each of the surface-coating layer and the
Sn-containing oxide layer, the thickness of each of the
surface-coating layer and the Sn-containing oxide layer in the
prepared thin film for cross-section observation was measured at
three locations, and the average value of the three locations was
set as the average thickness of the corresponding one of the
surface-coating layer and the Sn-containing oxide layer.
Here, the composition of each of the surface-coating layer and the
Sn-containing oxide layer was identified by an energy-dispersive
X-ray spectrometer (EDX), X-ray diffractometer (XRD), laser Raman
spectrometer, and/or Fourier transform infrared spectroscopic
analyzer used in the SEM observation or TEM observation.
(Plating Bath Composition and Plating Condition of Strike
Layer)
<Ni strike>
Nickel chloride: 240 g/L
Hydrochloric acid: 125 ml/L
Temperature: 50.degree. C.
<Ni-P strike>
Nickel sulfate: 1 mol/L
Nickel chloride: 0.1 mol/L
Boric acid: 0.5 mol/L
Sodium phosphite: 0.05 mol/L to 5 mol/L
Temperature: 60.degree. C.
<Cu strike>
Copper cyanide: 30 g/L
Sodium cyanide: 40 g/L
Potassium hydroxide: 4 g/L
Temperature: 40.degree. C.
<Ag strike>
Silver potassium cyanide: 2 g/L
Sodium cyanide: 120 g/L
Temperature: 30.degree. C.
<Au strike>
Gold potassium cyanide: 8 g/L
Sodium citrate: 80 g/L
Nickel sulfamate: 3 g/L
Zinc acetate: 0.3 g/L
Temperature: 30.degree. C.
(Plating Bath Composition and Plating Condition of Surface-Coating
Layer)
<Au>
Gold potassium cyanide: 8 g/L
Sodium citrate: 80 g/L
Nickel sulfamate: 3 g/L
Zinc acetate: 0.3 g/L
Temperature: 30.degree. C.
Current density: 1 A/dm.sup.2
<Ni.sub.3Sn.sub.2>
Nickel chloride: 0.15 mol/L
Tin chloride: 0.15 mol/L
Potassium pyrophosphate: 0.45 mol/L
Glycine: 0.15 mol/L
Temperature: 60.degree. C.
Current density: 1 A/dm.sup.2
<TiN-dispersed Ni.sub.3Sn.sub.2>
Nickel chloride: 0.15 mol/L
Tin chloride: 0.15 mol/L
Potassium pyrophosphate: 0.45 mol/L
Glycine: 0.15 mol/L
Temperature: 60.degree. C.
Current density: 1 A/dm.sup.2
Average particle size of dispersed TiN: 1.5 .mu.m
In the disclosure, as long as a desired plating can be formed, a
plating bath composition other than the above may be used according
to a known plating method.
Table 1 summarizes the results of evaluating the corrosion
resistance (stability in the separator use environment) and the
adhesion property for each sample obtained as described above.
TABLE-US-00001 TABLE 1 Sample preparation condition Strike layer
Current Electroplating Coating ratio of Maximum diameter of Sample
density time strike layer island-like coating portion P content No.
Substrate Type (A/dm.sup.2) (sec) (%) (.mu.m) (mass %) 1 Stainless
steel N/A -- -- -- -- -- 2 SUS447J1 Ni 6 1 2 0.01 -- 3 5 3 31 0.04
-- 4 3 20 62 0.08 -- 5 2 35 70 0.22 -- 6 3 50 100 Connected and
unmeasurable -- 7 Ni--P 7 1 5 0.02 13 8 6 1.5 11 0.03 14 9 6 2.5 27
0.04 15 10 3 5 27 0.11 15 11 2.5 6 27 0.21 15 12 2 7.5 27 0.54 15
13 1.5 10 27 0.93 15 14 1 15 27 1.60 15 15 6 6 42 0.02 15 16 5 10
50 0.07 15 17 1 80 67 1.00 16 18 2 50 75 0.80 16 19 1 130 86 1.60
16 20 3 60 100 Connected and unmeasurable 17 21 Cu 4 2 25 0.04 --
22 4 4 38 0.08 -- 23 Ag 4 3 30 0.06 -- 24 4 7 48 0.10 -- 25 Au 4
1.5 16 0.04 -- 26 4 3 33 0.06 -- 27 Ni 5 2.5 25 0.04 -- 28 Ag 5 1.5
18 0.03 -- 29 1 80 84 0.80 -- 30 N/A -- -- -- -- -- 31 Ni--P 6 2 20
0.03 15 32 1 130 86 1.60 16 33 Ni 6 1 2 0.01 -- 34 6 1 2 0.01 -- 35
2 40 74 0.30 -- 36 Ni--P 6 2 20 0.04 15 37 1 130 86 1.60 16 38
Ni--P 6 2 20 0.04 15 39 2.5 25 55 0.20 16 40 Au 4 1.5 16 0.04 -- 41
Ni 5 2.5 25 0.04 -- 42 2 40 74 0.30 -- 43 Ni 5 2.5 25 0.04 -- 44
1.5 60 80 0.50 -- 45 Titanium N/A -- -- -- -- -- 46 JIS 1 type Ni 5
2.5 28 0.04 -- 47 Ni--P 6 2 24 0.03 15 48 Cu 4 2 25 0.05 -- 49 Ag 4
3 30 0.06 -- 50 Au 4 1.5 20 0.04 -- Sample preparation condition
Surface-coating layer Sn-containing oxide layer Average Average
Sample thickness Main thickness No. Type (.mu.m) Formation method
component (nm) 1 Au 3.0 Plating -- -- 2 1.0 -- -- 3 1.0 -- -- 4 1.0
-- -- 5 1.0 -- -- 6 1.0 -- -- 7 1.0 -- -- 8 1.0 -- -- 9 1.0 -- --
10 0.5 -- -- 11 1.0 -- -- 12 3.0 -- -- 13 1.0 -- -- 14 1.0 -- -- 15
1.0 -- -- 16 1.0 -- -- 17 1.0 -- -- 18 1.0 -- -- 19 5.0 -- -- 20
1.0 -- -- 21 1.0 -- -- 22 1.0 -- -- 23 1.0 -- -- 24 1.0 -- -- 25
1.0 -- -- 26 1.0 -- -- 27 Carbon black- 10.0 Firing after
application -- -- 28 dispersed epoxy resin 5.0 -- -- 29 5.0 -- --
30 Graphite-dispersed 3.0 Firing after application -- -- 31 phenol
resin 5.0 -- -- 32 5.0 -- -- 33 Diamond-like carbon 0.3 CVD -- --
34 1.0 -- -- 35 0.1 -- -- 36 TiN-dispersed 2.0 Plating -- -- 37
Ni.sub.3Sn.sub.2 5.0 -- -- 38 SnO.sub.2 0.1 PVD -- -- 39 0.1 -- --
40 TiO.sub.2 0.1 PVD -- -- 41 TiN 0.1 PVD -- -- 42 0.1 -- -- 43
Polyaniline 1.0 Electropolymerization -- -- 44 1.0 -- -- 45
Ni.sub.3Sn.sub.2 3.0 Plating SnO.sub.2 15 46 1.0 -- -- 47 1.0
SnO.sub.2 15 48 1.0 SnO.sub.2 15 49 1.0 SnO.sub.2 15 50 1.0
SnO.sub.2 15 Total electric Evaluation result charge for 100
Peeling of surface- Corrosion Sample hours coating layer in tape
resistance after 100 No. (mC/cm.sup.2) removal test hours Adhesion
Remarks 1 12.3 Peeled Excellent Poor Comparative Example 2 14.0 Not
peeled Excellent Good Example 3 16.1 Not peeled Good Good Example 4
17.4 Not peeled Good Good Example 5 18.8 Not peeled Good Good
Example 6 398 Not peeled Poor Good Comparative Example 7 12.6 Not
peeled Excellent Good Example 8 12.8 Not peeled Excellent Good
Example 9 13.5 Not peeled Excellent Good Example 10 15.6 Not peeled
Good Good Example 11 15.8 Not peeled Good Good Example 12 18.0 Not
peeled Good Good Example 13 19.5 Not peeled Good Good Example 14
334 Not peeled Poor Good Comparative Example 15 15.1 Not peeled
Good Good Example 16 16.3 Not peeled Good Good Example 17 20.5 Not
peeled Good Good Example 18 165 Not peeled Poor Good Comparative
Example 19 211 Not peeled Poor Good Comparative Example 20 384 Not
peeled Poor Good Comparative Example 21 12.3 Not peeled Excellent
Good Example 22 13.2 Not peeled Excellent Good Example 23 12.5 Not
peeled Excellent Good Example 24 13.1 Not peeled Excellent Good
Example 25 12.0 Not peeled Excellent Good Example 26 12.4 Not
peeled Excellent Good Example 27 65.5 Not peeled Good Good Example
28 72.8 Not peeled Good Good Example 29 119 Not peeled Poor Good
Comparative Example 30 56.7 Peeled Good Poor Comparative Example 31
67.7 Not peeled Good Good Example 32 216 Not peeled Poor Good
Comparative Example 33 69.9 Not peeled Good Good Example 34 34.9
Not peeled Good Good Example 35 219 Not peeled Poor Good
Comparative Example 36 64.1 Not peeled Good Good Example 37 211 Not
peeled Poor Good Comparative Example 38 1.1 Not peeled Excellent
Good Example 39 113 Not peeled Poor Good Comparative Example 40 1.5
Not peeled Excellent Good Example 41 32.5 Not peeled Good Good
Example 42 174 Not peeled Poor Good Comparative Example 43 54.5 Not
peeled Good Good Example 44 194 Not peeled Poor Good Comparative
Example 45 9.9 Peeled Excellent Poor Comparative Example 46 38.5
Not peeled Good Good Example 47 11.4 Not peeled Excellent Good
Example 48 10.9 Not peeled Excellent Good Example 49 10.7 Not
peeled Excellent Good Example 50 10.1 Not peeled Excellent Good
Example
The table reveals the following points.
(a) The samples of Examples all had low current density after 100
hours in the corrosion resistance evaluation, and had favorable
corrosion resistance even in the event of long exposure to high
potential as in the separator use environment. In particular, Nos.
2, 7 to 9, 21 to 26, 38, 40, and 47 to 50 had excellent corrosion
resistance. Moreover, the samples of Examples all had excellent
adhesion property.
(b) The samples of Comparative Examples Nos. 1, 30, and 45 with no
strike layer did not have desired adhesion property.
(c) The samples of Comparative Examples Nos. 6, 14, 18 to 20, 29,
32, 35, 37, 39, 42, and 44 with the coating ratio of the strike
layer on the substrate and/or the maximum diameter of the
island-like coating portion being outside the appropriate range had
high current density after 100 hours in the corrosion resistance
evaluation, and did not have desired corrosion resistance.
REFERENCE SIGNS LIST
1 membrane-electrode joined body 2, 3 gas diffusion layer 4, 5
separator 6 air passage 7 hydrogen passage
* * * * *